Using observations to improve surface boundary conditions for large-scale ice sheet models of Greenland

Improving surface boundary conditions for large-scale ice sheet models of Greenland is the main focus and simple parameterizations are used to calculate surface melt, snow densification and meltwater retention. Near-surface air temperature (2m) and its standard deviation from the monthly means over the Greenland Ice Sheet (GrIS) are parameterized using data from automatic weather stations (AWS) located on land and on the ice sheet. The parameterizations are used in a surface mass balance model based on a positive degree day (PDD) approach to simulate the present-day mean surface elevation of the GrIS. The PDD approach accounts for firn warming, rainfall, and refreezing of melt water, with different PDD-factors for ice and snow under warm and cold climate conditions. The snow densification and meltwater retention processes achieves a separation of volume and mass changes of the surface layer to determine the surface melt contribution to runoff. Based on experiments for present-day conditions the simulated surface elevation is found to have a reasonable agreement with observations.